Osteoarthritis is a pathologic condition in synovial joints characterized by cartilage extracellular matrix degradation. A major component of cartilage extracellular matrix is the proteoglycan aggrecan. Pathologic cleavage of aggrecan occurs at 2 primary sites within the interglobular domain of the protein backbone which results in release of the functional entity from the extracellular matrix. One site (N341-342F) is cleaved by matrix metalloproteases (MMPs), while a second, non-MMP cleavage site within aggrecan is at E373-374A. The E373-374A cleavage site has been identified as an important site of degradation in osteoarthritic synovial fluid samples (Lohmander, Neame and Sandy, 1993, Arthritis & Rhuem 36:1214) and cytokine stimulated cartilage cultures (Sandy et al., 1991, J. Biol. Chem. 266:8683). Several ADAMTS enzymes have been demonstrated to be capable of cleaving aggrecan at the E373-374A, or “aggrecanase” site (Kuno et al., 2000, FEBS Letters 478 :241; Rodriquez-Manzaneque et al., 2002, Biochem. Biophys. Res. Commun. 293:501; Somerville et al., 2003, Biol. Chem. 278:9503; U.S. Pat. No. 6,451,575). ADAMTS-4 and ADAMTS-5, or Aggrecanase-1 and Aggrecanase-2, respectively, appear to be the two enzymes capable of being synthesized by articular cartilage with by far (>1000 fold) the most efficient “aggrecanase” activity (Tortorella et al., 1999, Science 284:1664; and Abbaszade et al., 1999, J. Biol. Chem. 274:23443). However, it is not clear whether these enzymes, either collectively or independently, are responsible for the aggrecan degradation in osteoarthritis.
Evidence of ADAMTS-4 in joint disease is found in several reports of increased expression of ADAMTS-4 after stimulation of articular tissues with inflammatory cytokines. Bau et al., 2002, Arthritis & Rhuem 46:2648-2657; Curtis et al., 2000, J. Biol. Chem. 275:721-724; Tortorella et al., 2001, Osteoarthritis Cartilage 9:539-552; Little et al., 2002, Arthritis & Rhuem 46:124-129; and Yamanashi et al., 2002, J. Immunol. 168:1405-1412. In vitro findings indicate that ADAMTS-4 is one of the few enzymes that can efficiently cleave aggrecan at the site that is cleaved in naturally occurring disease. Tortorella et al., 2000, J. Biol. Chem. 275:18566-18573; Tortorella et al., 2002, Matrix Biol. 21:499-511.
In addition, aggrecanases are known to play a role in other disorders in which extracellular protein degradation or destruction occurs, such as cancer, asthma, chronic obstructive pulmonary disease (“COPD”), atherosclerosis, age-related macular degeneration, myocardial infarction, corneal ulceration and other ocular surface diseases, hepatitis, aortic aneurysms, tendonitis, central nervous system diseases, abnormal wound healing, angiogenesis, restenosis, cirrhosis, multiple sclerosis, glomerulonephritis, graft versus host disease, diabetes, inflammatory bowel disease, shock, invertebral disc degeneration, stroke, osteopenia, and periodontal diseases.
The generation of the ADAMTS-4 knockout (KO) has previously been reported (Glasson et al., 2004, Arthritis and Rheum, 50:2547-2558). While many reports showed at least some evidence that ADAMTS-4 is involved in the development of osteoarthritis, surprisingly this mouse did not show any differences in the onset of osteoarthritis than wild-type (WT) and did not exhibit any difference in aggrecanase activity. Although, it is still possible that ADAMTS-4 is involved in osteoarthritis in other animals, including humans, to date, the aggrecanase activity associated with the pathological accumulation of aggrecan degradation products has not been identified.